Mercury 300 HP ProXS V8 Electric Start Steering Trim Tilt Extra Long Shaft Outboard Motor

The Mercury 300 XL ProXS V8 is a 4-stroke outboard marine engine designed for sport fishing boats requiring an extra-long shaft, speed-focused fiberglass boats, and performance-oriented users. It features a 300 HP / 224 kW and 4600 cc V8 (8 Cylinder) engine. The ProXS series is Mercury's lineup that offers optimized high-performance configurations compared to standard FourStroke engines. It is developed for boat use prioritizing speed and responsiveness, with a high RPM range and performance-focused fine-tuning.

300 XL ProXS V8 Series Features and Technology Advantages

ProXS models operate in a higher RPM range compared to their standard FourStroke counterparts. Performance-oriented ECU calibration shifts the power band to higher RPMs, increasing responsiveness and top speed.

• V8 (8 Cylinder) Engine (4600 cc): ProXS models operate in a higher RPM range compared to their standard FourStroke counterparts.
• Extra-Long Shaft (572 mm (22.5")): Propeller operates at optimum depth with correct transom height.
• ProXS Performance Configuration: Enhanced responsiveness and maximum speed with a high RPM range and optimized ECU calibration.
• Electric Start: Instant activation with key or button — comfortable and quick starting.
• Power Trim & Tilt: Adjust trim angle with a button while cruising — optimizes fuel efficiency; fully raise the engine with tilt.
• External Floating Fuel System: Connection for large-capacity external tank — range determined by user needs.

Extra-Long Shaft — Which Boat Type Is It Suitable For?

An extra-long shaft (572 mm (22.5")) allows the propeller to operate at the correct water depth on large, high-sided fiberglass and aluminum boats. It is 64 mm longer than the standard long shaft (508 mm).

Technical Specifications

Who Is This Engine For?

• Sport fishing boats: fast planning and quick positioning with a high RPM range.
• Performance-oriented fiberglass boats: increased responsiveness and speed with ProXS calibration.
• Tournament fishing: fast relocation and efficient fuel use.
• Boat owners who want speed and performance: a superior performance tier compared to standard FourStroke.

Maintenance and Longevity

4-stroke Mercury engines operate smoothly for many years with regular oil changes and end-of-season maintenance protocols. The impeller of the water-cooled system should be checked every 100 hours or every two seasons. In saltwater use, fresh water rinsing is mandatory after each use.

Related maintenance categories: Maintenance Kit | Engine Oil | Impeller | Mercury Spare Parts

Frequently Asked Questions

What is the difference between ProXS and standard FourStroke 300 HP?

ProXS models offer the same engine block with a higher RPM range and performance-oriented ECU calibration. Compared to the standard model, it provides a higher maximum RPM, increased responsiveness, and superior top speed performance. Fuel consumption might be slightly higher at wide-open throttle.

Which propeller works best with a ProXS engine?

Since ProXS models are optimized for a high RPM range, a propeller with a lower pitch is generally preferred. Propeller selection should be determined by a Mercury service technician based on boat type, weight, and the desired balance of speed and acceleration.

Are ProXS maintenance requirements different from standard FourStroke?

Basic maintenance requirements are similar: regular oil changes, impeller checks, and end-of-season maintenance. However, due to high RPM use, more attention to oil quality is recommended. Service intervals should be followed according to manufacturer recommendations.

Which boat and hull brands are compatible with the 300 XL ProXS V8?

Mercury outboard motors are compatible with many fiberglass, aluminum, and inflatable boat models thanks to their universal transom clamp or transom mounting system. The only criteria are your boat's 572 mm (22.5") transom height and the maximum engine power approved by the manufacturer. You can get compatibility confirmation from Clever Marin by sharing your boat model.

Related Products and Categories

• Mercury Outboard Motors
• Mercury Marine Products
• Mercury Spare Parts
• Mercury ProXS 115–150 HP
• Mercury 175–300 HP FourStroke
• Outboard Motors
• Boat Engines
• Maintenance Kit
• Impeller
• Anode

Is This the Right Configuration for Your Boat?

Share your boat model, transom height, and intended use — let's verify together if the Mercury 300 XL ProXS V8 engine is suitable for your boat and ensure the correct shaft selection.